1. Field of the Invention
This invention relates to .beta.-lactam derivatives represented by the formula (I) hereinafter defined and the pharmaceutically acceptable salts thereof which are useful as antimicrobial agents, a process for preparing the same and a pharmaceutical composition containing .beta.-lactam derivatives.
2. Description of the Prior Art
It is known that certain types of polyheterocyclic compounds exhibit antimicrobial activity. For example, U.S. Pat. No. 3,917,609 to Gerster et al discloses substituted derivatives of 1,2-dihydro-6-oxo-6H-pyrrolo[3,2,1-ij]quinoline which are useful as antimicrobial agents or as intermediates for the preparation of antimicrobial agents.
Also, U.S. Pat. Nos. 3,896,131, 3,985,882, 3,969,463, 4,001,243 and 4,014,877 to Gerster et al disclose 6,7-dihydro-1-oxo-1H, 5H-benzo[ij]quinolizine derivatives having antimicrobial activities.
However, the .beta.-lactam derivatives of the present invention are structurally different from these quinoline and quinolizine compounds. Further, the .beta.-lactam derivatives of the present invention have a potent antimicrobial activity against various bacteria, especially Pseudomonas aeruginosa.